Using the facilities of the Computer Graphics Laboratory, we are working on modelling the substrate binding sites of new granzyme serine proteases, based on the X-ray crystal structure of rat mast cell chymase II, another serine protease. Knowledge of potential substrates will allow them to be synthesized and tested to determine if the granzyme gene products are active enzymes. These proteases are in cytotoxic granules of killer cells and probably play critical roles in killing of virally infected cells and/or in signalling for inflammation.